An estuarine fossil assemblage from the Yacoraite Formation (Maastrichtian-Danian) and its paleoenvironmental significance. Jujuy - Northwestern Argentine

CARLOS A. CÓNSOLE GONELLA,HORTA L.R., HERRERA OVIEDO P.E., GRIFFIN M., GEORGIEFF S.M. AND F.G. ACEÑOLAZA

San Miguel de Tucumán

Congreso; 9th INTERNATIONAL CONFERENCE ON FLUVIAL SEDIMENTOLOGY; 2009

Fundación Miguel Lillo

We describe a brackish water fossil assemblage from the Yacoraite Formation (Maastrichtian – Danian), exposed in the environs of Maimará and Jueya, province of Jujuy - Northwestern Argentina. Dominant lithology of the studied rocks is characterized by a succession of fining-upward, calcareous sandstones, with ripplestratified structure. Interstratified are also lenses of fine to very fine sandstone. The sandstones are interpreted as storm washover deposits. In these sequences we found numerous disarticulated remains of fish (Pycnodontiformes and Siluriformes), fragments of tetrapods? (Tetrapoda), a crocodile tooth (Crocodylidae), preserved mollusks (Gastropoda and Bivalvia) of problematic identification, stromatoliths (LLHC, LLHS and dome type). Also identified was a set of fossil traces comprising traces of birds (Avipedidae) and Skolitos ichnofacies, besides a pholadid boring in a stromatolithic rock, including preserved the bivalve shell. Study of the fossil assemblage, traces, sediments, and sedimentary structures indicates a shallow, high energy, mixed, and probably estuarine brackish environment.